I’m currently writing a procedure and was taking various SPI waveforms. In general, all of the waveforms look good, but noticed that when I send 0x00 33 40 the MOSI (blue waveform) signal goes to intermediate levels at times. Is this a concern?
The spi is set to mode 2, CS active low.
Thanks
Is it noise?
I don’t think so. Since its mode 2, I’m not even positive its an issue because the downward clock edge always has the value I’d expect, its just the in between edges that look odd. Again, its only for this message which is the weird part to me. See these other messages from exact same bus with exact same code that do not show the same characteristics.
is this software installed on PC?
I have run it in debug mode directly from visual studio, or just simply run the firmware by itself with the breakout powered through the barrel jack. Both yield the same result.
Sorry my question wasn’t clear.
I mean the oscilloscope tool you are using.
I don’t think your issue relates to SPI or SITCore software.
Its a benchtop tektronix 2000B scope.
Pick one of your SPI pins above, set it to GPIO output and toggle that pin. Of course you can’t use SPI if you are going to make it become output mode.
I think you will see same issue.
Then pick any other pin, this pin should not connect to any thing, make output and toggle that pin.
If this pin clean mean your slave SPI has issue.
If you still have same result, something with noise or not sure yet :)).
I just gave it a shot with a different scope and am not able to reproduce the issue. Maybe not happening right now, maybe a scope issue. Anyway, do appreciate your help on this.
From the looks of these signals, your power supply does seem to be producing classic switch-mode noise. Some cheap switch-mode power supplies will notably produce a great deal more noise as the current draw increases.
If I’m reading the display right, it’s set to 2V/division and by the looks of the noise its pk-to-pk is close to 2V at times. While I don’t think this is the actual cause of the enumerated problem, it is cause for concern, especially for high-speed 3.3V SPI.
Those - half state waveforms might indicate a weak gate or a ground-ref problem.
in any case, the low-hanging fruit here is:
Use a battery for your power supply when checking timings and bit-bashing data in and out of SPI. It’ll save you some headaches.
Make sure you have a decent ground here. You can check this using a sensitive DVM placed between the DUT ground and the test equipment ground. Any voltage differential is bad news. (I once found a 120VAC difference this way - someone reverse-wired a strip where a CP/M multiuser box was blown sky-high after plugging in an RS232 cable from a Televideo 920 in another room.)
Good luck!
